Prior art of possible relevance includes U.S. Pat. No. 3,989,407 issued Nov. 2, 1976 to Cunningham and, conceivably, U.S. Pat. No. 4,417,848 issued Nov. 29, 1983 to Dembeck.
As is well known, turbine wheels utilized in turbines of various sorts frequently operate at extremely high rotational speeds. Any of a variety of occurrences can cause the breakage of turbine blades forming part of the turbine wheels. For example, ingestion of foreign material into the turbine can cause such breakage. Similarly, fatigue of the turbine blades, frequently introduced by thermal forces may, cause breakage of one or more turbine blades. In a like vein, excessive wear on bearings journalling the turbine wheel may lead to interference between fixed and rotating components of the turbine which in turn can cause breakage of blades.
Because of the high rotational velocities at which such wheels frequently turn, the blades contain considerable stored energy which is released upon breakage of one or more of the blades. The centrifugal force will cause the blade fragment to travel radially outwardly at high velocity which is sufficient to pierce the relatively thin housing for the turbine and exit the same while still at very high velocity. Not infrequently, in the course of movement, the separated fragment of a blade will be deflected by other turbine components such that its path of travel will have an axially directed component as well as a radially directed one. In any event, such fragments, whether traveling purely radially, or purely axially, or both radially and axially, have the capacity to severely damage other objects in the vicinity of the turbine.
To avoid this problem, various so-called "containment" proposals have evolved. The object of such proposals is to prevent the escape of separated turbine blade fragments at high velocity from the turbine in the radial, or axial, or both directions.
Radial confinement is frequently effected by a so-called containment ring. Typically, a containment ring is a relatively thick ring of material capable of withstanding high impact loads. The same is disposed about the turbine blades just radially outwardly of the peripheries thereof and in axial alignment therewith. A radially inwardly opening groove is located on the inner periphery of the ring in facing relation to the ends of the turbine blades. Radially traveling separated blade fragments move radially outwardly to impact against the ring at the bottom of the groove and the walls of the groove prevent substantial axial deflection of the separated fragments.
Heretofore, many proposals for containment rings utilize bolts for securing the ring in axial alignment with the blades. In many instances, particularly where weight is of concern as in aircraft applications, to save weight, the components are made as small and as compact as possible. Thus, in systems such as shown in the previously identified Cunningham patent, locating bolts may be in fairly close proximity axially speaking to the blades such that a blade fragment traveling principally in the radial direction but having an axial component of movement can impact against the bolts to shear the same. Additionally, the ring location housings may deform and separate. In either event, the containment ring can no longer be positively located in axial alignment with the blades. If the ring then becomes misaligned, it can no longer provide radial containment. Moreover, such constructions as are known in the prior art universally require provision of separate means to provide axial containment.
The present invention is directed to overcoming one or more of the above problems.